ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 1041 



The author regards the cause of the motion to be the exudation of 

 mucilage, which does not take place uniformly and simultaneously 

 from the whole surface of the desmid. This is not, however, here, as 

 it is elsewhere, a result of the disintegration of the cell-wall itself; it 

 is derived directly from the cytoplasm, and passes through the cell- 

 wall without the latter undergoing any change. Many species are 

 completely surrounded by a gelatinous envelope, while others are 

 comparatively free. 



Internal Spore-formation in Diatoms.* — Count Ab. F. Castracane 

 describes a remarkable appearance in a deposit of marine diatoms of 

 pliocene date from the Apennines. In a specimen of Coscinodiscus 

 pundulatus he observed that the lower part of the valve, minutely 

 punctuated in a radial disposition, showed small round uniform 

 stalked bodies ; the drawing under the camera lucida exhibiting 

 clearly the circular iigiare. No other interpretation seems possible 

 of these minute round bodies, always found in the interior of the 

 frustule, excei)t that they constitute a nest of embryonal diatoms on 

 the point of escaping from the mother-cell. This is in accord with 

 previous observations of the author on similar round bodies seen on 

 tl e point of escaping from a Podosvhenia, and with observations of 

 Kabenhorst and O'Meara. The fact that the diatoms in which these 

 bodies were observed liad previously been treated with boiling sul- 

 phuric acid with addition of jDotassium clilorate, shows conclusively 

 that the round corpuscles seen to escape from living diatoms are not 

 Infusoria or other organisms fortuitously collected round them, and 

 demonstrates at the same time that, from the first moment of their 

 existence, diatoms must be provided with a siliceous coating, though 

 it may be of extreme tenuity. 



It would seem tlien that a diatom may assume the function of a 

 sporangium, producing in its interior embryonal forms by which the 

 species is reproduced, and w'hich ultimately acquire the form and 

 approximately the size of the mother-frustule. 



Mysterious Appearance of a Diatom.f — Mr. F. Kitton finding 

 on carafes of water a film composed entirely of frustules of Achnanthcs 

 linearis, and having never found it on the filter i>ai>ers used in filter- 

 ing the water, filtered 8 oz. of the water into a glass-stoppered bottle, 

 using a filter paper 1 in. in diameter and a very small glass funnel. 

 When the bottle was filled the paper was boiled in sulphuric acid and 

 decarbonized, the residuum giving no indications of diatomacoous 

 remains. In the course of a few days the film began to apjiear on 

 the bottle, and was found to consist of the above-named diatom un- 

 mixed with any other form. As this is a very minute 8i)ecies 

 (0-0004 in. in l(;ngth and less than 0'0002 in. in breadth), he thought 

 it just possible that some of the frustules might have passed through 

 the i)aper, but on filtering some emery-powder which had remained 

 in suspension six or seven hours, and the particles of which were less 

 than 0*00005 in. in size, these were found not to pass through the 



• Accatl. Pohtif. de" Niiov. Line, xxxviii. (inHf)) Sobs. May 17, pp. 7-8. 

 t .Fourri. Qu«;k. Wwr. Club, ii. (IHH.^j) jij). MH-'J and 'iOO. 



